On Wednesday, November 27, 2013 9:06:43 AM UTC-5, TimR wrote:
I asked the question about a multiple tap transformer because I don't understand the details about how a part of a circuit gets "out of phase."



We're using the word phase in several different ways and that's part of the confusion at least for me.



I'm not sure it makes sense to say the two lines of a 240 volt service are 180 degrees out of phase even if technically they are, because that seems to imply a two phase supply, and that you can create an infinite number of phases with a multiple tap transformer.



See the new thread I just started on electrical phases. I laid
out an interesting exercise in looking at phase, where I start out
with what everyone here agrees is 3 phase and morph it into two
phase and it's identical, indistinguishable, from split-phase 240/120V.





In my blissful ignorance I just always considered one line to be +120 volts referenced to ground, and the other -120 volts. I'm pretty sure that's wrong, but at least it's not confusing.


It's not wrong. But when you have a periodic waveform and one
wave is the inverse of the other, it's also referred to as an 180 deg
phase difference. That one leg is 180 deg out of phase with the other.
And if you look at those two waveforms on a scope, that is what you see.

Here from white papers from electrical eqpt manufacturers:

http://www.samlexamerica.com/support...Circuit s.pdf

http://www.behlman.com/applications/AC%20basics.pdf



I admit I don't understand the fine details here. So, suppose I take my 120 volt singlephase house current, and I connect two incandescent light bulbs in series, each with a resistance of 60 ohms. Total resistance is now 120 ohms so I should have 1 ampere of current flowing. If I measure the voltage across both bulbs I should have 120 volts; but if I measure from between the two light bulbs in either direction I will read 60 volts (and the bulbs won't be all that bright). (but I don't care, I'm not going to read by them; this is a thought experiment)



NOW: are those two voltages 180 degrees out of phase? If not, why not?

If you look at the ends of the two bulbs referenced to the mid-point,
then yes. When one is +60, the other will be -60. You could hook up
a scope, use the center as the reference, put one probe on the top of
one bulb, the other on the bottom of the other bulb and you'd see two sine waves, 180 deg out of phase. The disagreement is that those on the other
side of this refuse to call that a phase difference. They say it's just
180 deg opposite. Well, when you have two sine waves that are the opposite
of each other, their phase relationship is that they are 180 deg apart.
Which is why I've asked those on the other side 10 times to simply define
the term phase. Yet despite telling me that I'm the one that is
confused, not one of them can define it. How can you speak about
something and not be able to define it?


This is exactly analogous to the center tapped transformer, with the sole exception that I didn't ground the center of the lightbulb circuit.



What if I used 4 bulbs? Etc.

If you use 4 bulbs in series and used the center point as a reference,
you would see +30V, +60V, -30V, -60V again with the sine waves 180 deg
out of phase.